If you're planning on going SLI, keep the reference cards - non reference ones do worse in SLI as they exhaust hot air into the case and heat each other up, while reference cards exhaust hot air outside of the case.

One gtx 580 is plenty for a single 1080p monitor, probably more than enough. Two gtx 580's is so overkill it's not even funny. The only point of more than one gtx 580 is if you wanted to do triple screens, or play at resolutions of 2560x1440/1600.

I got 580 and 3d monitor never used the3d part. got it for 120hz better gameplay
My 580 is a reference Overclocked to 950core. hit 55 degs C and its 92 degs F outside
I got a water block on mine. Swap over to water or but the cash into case and wait till after married and say a buddy bout u it delayed wedding gift. that what my buddy dose . He been married 5 years